1. Field of the Invention
This invention relates generally to high speed data communications.
2. Description of the Related Art
Optical fiber is widely used as a communications medium in high speed digital networks, including local area networks (LANs), storage area networks (SANs), and wide area networks (WANs). There has been a trend in optical networking towards ever-increasing data rates. While 100 Mbps was once considered extremely fast for enterprise networking, attention has recently shifted to 10 Gbps, 100 times faster. As used in this application, 10 Gigabit (abbreviated as 10G or 10 Gbps or 10 Gbit/s) systems are understood to include optical fiber communication systems that have data rates or line rates (i.e., bit rates including overhead) of approximately 10 Gigabits per second. This includes, for example, LRM and SFF-8431, a specification currently under development by the SFF Committee that will document the SFP+ specifications for 10G Ethernet and other 10G systems.
Recent developments in 10G optical communications have included the use of Electronic Dispersion Compensation (EDC) in receivers to extend range. For example, the IEEE 802.3aq standards committee has developed a standard (10 GBASE-LRM or simply LRM) for 10G Ethernet over multi-mode fiber over distances of up to 220 meters using EDC. This standard is documented in IEEE Std. 802.3aq-2006 (IEEE Standard for Information technology—Telecommunications and information exchange between systems—Local and metropolitan area networks—Specific requirements, Part 3: Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Access Method and Physical Layer Specifications, Amendment 2: Physical Layer and Management Parameters for 10 Gb/s Operation, Type 10 GBASE-LRM), referred to herein as IEEE 802.3aq-2006 or LRM, and incorporated by reference.
However, there are many challenges to implementing 10G systems, especially over multi-mode fibers. Multi-mode fibers generally are a high dispersion communications channel with a significant amount of variability from fiber to fiber, and even within the same fiber over a period of time. In addition, one of the first components in a receiver is the analog to digital converter (ADC). However, a 10G system requires a 10G ADC, which can be difficult and expensive to build with the required resolution. More generally, various other components in the receiver may also be difficult or expensive to build at this speed of operation. In some instances, high-speed operation can be achieved by moving to more complex circuit designs or less frequently used materials (e.g., GaAs). However, added complexity often comes at the price of higher cost or lower reliability. The use of different materials systems may increase the cost by increasing the overall count of integrated circuits if the materials systems cannot be combined on a single integrated circuit.